Not applicable.
Not applicable.
Not applicable.
A gun barrel is subjected to significant forces when a bullet is fired through it. The exploding powder in the shell casing drives the bullet from the shell casing and accelerates it through the barrel. Incrementally with each round of ammunition, the barrel is subjected to erosive action toward the chamber end and abrasive action toward the muzzle end. Repeated rounds fired through the barrel eventually take their toll and the accuracy of the gun begins to decline.
Barrels can be made of more exotic materials to address this problem. These materials extend the life of the barrels but with a corresponding increase in cost, perhaps to prohibitive levels for any production gun. Alternatively, there have been a number of attempts to apply coatings to barrels or to insert liners to improve gun barrel durability. These attempts have met with varying degrees of success. The lining material, for example, being very hard, is typically brittle. It is therefore prone to developing cracks as a result of the insertion process.
Thus, there remains a need for a way to provide a durable and cost-effective barrel for a production-quantity gun intended for use in firing large numbers of rounds of ammunition.
The present invention is a method for lining a barrel. In particular, the present method applies best to those production level gun barrels intended for use in firing large numbers of rounds, such as machine guns. According to this method, a solid rod, or at most a solid rod with a small hole formed in it, made of a suitable liner material, is inserted into a barrel blank. The blank is then forged to the rod. Once forged, the rod is drilled to form the gun bore and rifled. The rod does not extend all the way through the barrel blank but only part way, beginning at the muzzle end and stopping at a xe2x80x9cstepxe2x80x9d formed inside the barrel blank near its chamber end.
Several aspects of this process are important. The first is that the surface of the rod is preferablyroughened or knurled to assure fusing of the blank metal into the metal liner. This ensures structural integrity of the assembly during firing. In addition, pressure is applied to the rod so that it maintains its seat against the step formed inside the barrel blank during forging. This pressure, along with the knurled surface of the rod, helps to maintain the correct position of the rod in the barrel during forging. These measures also help to assure that there is no gap between the liner and the barrel seat.
The location of the step inside the barrel is also important. It is preferably located adjacent to the location where a shell casing would be, if fully seated in the chamber, so that the step is covered by the shell casing, but not located so far toward the chamber end that the liner must be machined as part of the chamber. Also the step is located behind the shell case lip to ensure that hot gases do not flow onto the blank metal, but only onto the liner metal.
Another important part of the process is to begin with a solid or nearly solid rod of liner material. A nearly solid or completely solid rod distributes the stresses of forging better than a tube and results in greatly reduced cracking. To facilitate bore formation, a small holed can be formed in the liner before insertion or after forging, and does detract from the ability of the rest of the rod to distribute stresses.